Recently, a valve timing control device for an internal combustion engine has been provided that transmits the rotational force of an electric motor to a camshaft through a speed reduction mechanism to improve the control responsiveness and controllability of the relative rotational phase of a crankshaft and the camshaft.
For example, a valve timing control device described in the following Patent Literature 1 adopts a DC motor using brushes for a current application switching mechanism of a coil of the motor as an electric motor applied to generation of the rotational force. In the DC motor, a coil is wound around a rotor provided on the outer circumference of a motor shaft, and a permanent magnet is provided on the inner circumferential surface of a motor housing as a stator disposed opposed to the outer circumference of the rotor. It should be noted that a brush provided in a DC motor with a brush is referred to as a “first brush” in the following description. In addition, the motor shaft and the rotor are rotatably supported by bearings such as ball bearings. Further, as means to supply electric power to the DC motor, a mechanism configured using slip rings and a brush (hereinafter, referred to as a “second brush”) is used. Specifically, by adopting such a configuration, a camshaft can be rotated relative to a timing sprocket through a speed reduction mechanism by the rotational force of the motor.
Further, a DC motor with a brush to which a noise reduction part is connected is disclosed in the following Patent Literature 2 and Patent Literature 3 although the motor is applied to a fuel pump.